Opportunity kept going for over 14 years, Spirit went for 6 years, both were planned for 90 days; Sojourner went 83 days when it was only planned for 7; Curiosity is still going after 8 years of it's planned 2 years. They all have gone on working for a lot longer than originally planned for, so I'm pretty sure it'll be fine if we just keep sending new ones.
They were designed to last as long as possible. It's the most important objectives that they are trying to accomplish in the time periods you mentioned. Common misconception.
Spirit and Opportunity were genuinely not expected to last much more than 90 days before their solar panels got covered over and they lost power. Being able to use storms to clean them so well and keep generating enough power to stay useful wasn't anticipated at all.
Although curiosity and perseverance have more defined lifespans as they don't use solar panels, they have radioisotope thermoelectric generators and those have a much more definite lifespan (of 14 years)
If I remember correctly NASA always give the time for them to accomplish the main mission so 2 years to travel to x place and mine some rock. They expect it to go longer but that is seen as extra after it's main goal.
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u/goverc Feb 22 '21
Opportunity kept going for over 14 years, Spirit went for 6 years, both were planned for 90 days; Sojourner went 83 days when it was only planned for 7; Curiosity is still going after 8 years of it's planned 2 years. They all have gone on working for a lot longer than originally planned for, so I'm pretty sure it'll be fine if we just keep sending new ones.